Fun fact: Engelbert Humperdinck composed part of Wagner’s Parsifal. Shortly before the première, it was discovered that Wagner’s score didn’t allow time for a crucial scene change. The 27-year-old Humperdinck, then working as Wagner’s assistant, composed a few temporary bars to cover the gap and, rather to his own surprise, found that they met with the Master’s full approval: ‘Why not? It should work!’ It’s worth knowing partly because of the light it throws on the practical, collegial working methods of music’s favourite cartoon supervillain, and partly because it reaffirms the originality of Humperdinck’s own best-known opera, Hansel and Gretel....